What should I do if my teacher failed me because he simply doesn't like me?

so I have this teacher right he is hated throughout the whole school which is very small about 15 to 20 kids & they hate him because he is nosy & rude and he could joke around and make fun of you but god forbid you do of him_- The school secretary even hates him because she told me that he is so rude and that she cant stand him you see me and the secretary are close she is really nice to me and all the other student so in the beginng of the year I was passing with an A , I love his class because its my favorite subject … so even called me a teachers pet & I never got introuble with him he never kicked me out or anything which is why immature kids started saying he is inlove with me .. but that all changed when I started getting in trouble in other classes not his others … girls bugged me from the beginng of the year and I just started blowing up on them recently and I get introuble O.o which is not fair but anyways I do his work I do his homework he can ask me a question and I can answer it very quickly and very sure that my answer is right … I pass his test & on my last progress report he put my grade down as an A .. in the middle of class he asked me what grade do you think you have I said A he said yes .. so when I started getting introuble in the other classes he started to treat me different and when I got my reportcard yesterday in the mail he gave me a D ?!?!?! a D can you believe that I got a C in social studies and I hate that class I hardly do my work because I dont get it at points but I always do my homework and I got a C in that class but in my favorite subject that I do I go from an A to a D in what a week or something thats not possible he is failing me on purpose just like the other students what should I do?